1. Field of the Invention
The present invention relates to an ultrasonic probe for transmitting and/or receiving ultrasonic waves in an ultrasonic diagnostic apparatus for medical use or structure flaw detection, and specifically, to an ultrasonic probe suitable for wideband ultrasonic transmission and reception.
2. Description of a Related Art
In medical fields, various imaging technologies have been developed in order to observe the interior of an object to be inspected and make diagnoses. Especially, ultrasonic imaging for acquiring interior information of the object by transmitting and receiving ultrasonic waves enables image observation in real time and provides no exposure to radiation unlike other medical image technologies such as X-ray photography or RI (radio isotope) scintillation camera. Accordingly, ultrasonic imaging is utilized as an imaging technology at a high level of safety in a wide range of departments including not only the fetal diagnosis in the obstetrics, but also gynecology, circulatory system, digestive system, and so on.
The ultrasonic imaging is an image generation technology utilizing the nature of ultrasonic waves that the ultrasonic waves are reflected at a boundary between regions with different acoustic impedances (e.g., a boundary between structures). Typically, an ultrasonic diagnostic apparatus (or referred to as an ultrasonic imaging apparatus or an ultrasonic observation apparatus) is provided with an ultrasonic probe to be used in contact with the object or ultrasonic probe to be used by being inserted into a body cavity of the object. Alternatively, an ultrasonic endoscope is also used in which an endoscope for optically observing the interior of the object is combined with an ultrasonic probe for intracavity.
In the ultrasonic probe, for example, a piezoelectric vibrator having electrodes formed on both ends of a piezoelectric material is used as an ultrasonic transducer for transmitting and/or receiving ultrasonic waves. When a voltage is applied to the electrodes of the vibrator, the piezoelectric material expands and contracts to generate ultrasonic waves. Further, plural vibrators are one-dimensionally or two-dimensionally arranged and the vibrators are sequentially driven by drive signals provided with predetermined delays, and thereby, an ultrasonic beam can be formed toward a desired direction. On the other hand, the vibrator receives the propagating ultrasonic waves, and expands and contracts to generate an electric signal. The electric signal is used as a reception signal of ultrasonic waves.
Recently, in order to further bring out the usefulness of methods such as harmonic imaging, a demand for wider bandwidth has been made for an ultrasonic diagnostic apparatus, and there has been a problem of how to broaden the frequency characteristics of a vibrator to the wider bandwidth.
As a related technology, Japanese Patent Application Publication JP-P2006-320415A discloses an ultrasonic probe having wideband frequency characteristics and high sensitive characteristics adaptable to harmonic imaging for the purpose of uniforming the slice thickness of ultrasonic images and reducing side lobes. The ultrasonic probe has a piezoelectric vibrator unit in which plural piezoelectric layers including plural piezoelectric materials arranged in a scan direction are stacked with electrodes in between, and the piezoelectric material forming at least one piezoelectric layer within the plural piezoelectric layers is made of a composite piezoelectric material in which a piezoelectric material part and a non-piezoelectric material part are mixed.
Thereby, in a region where the non-piezoelectric material part and the piezoelectric layer are stacked, the sensitivity to high frequencies becomes higher than that in a region where the piezoelectric material part and the piezoelectric layer are stacked. However, the non-piezoelectric material part does not expand or contract when an electric field is applied, and thus, shearing stress may be generated between the non-piezoelectric material part and the piezoelectric layer and cracking may occur.